Jean-José Orteu

Image Correlation for Shape, Motion and Deformation Measurements

Image Correlation for Shape, Motion and Deformation Measurements provides a comprehensive overview of data extraction through image analysis. Readers will find and in-depth look into various single- and multi-camera models (2D-DIC and 3D-DIC), two- and three-dimensional computer vision, and volumetric digital image correlation (VDIC). Fundamentals of accurate image matching are described, along with presentations of both new methods for quantitative error estimates in correlation-based motion measurements, and the effect of out-of-plane motion on 2D measurements. Thorough appendices offer descriptions of continuum mechanics formulations, methods for local surface strain estimation and non-linear optimization, as well as terminology in statistics and probability. With equal treatment of computer vision fundamentals and techniques for practical applications, this volume is both a reference for academic and industry-based researchers and engineers, as well as a valuable companion text for appropriate vision-based educational offerings.

Metrology in a scanning electron microscope: theoretical developments and experimental validation

A novel approach for correcting both spatial and drift distortions that are present in scanning electron microscope (SEM) images is described. Spatial distortion removal is performed using a methodology that employs a series of in-plane rigid body motions and a generated warping function. Drift distortion removal is performed using multiple, time-spaced images to extract the time-varying relative displacement field throughout the experiment. Results from numerical simulations clearly demonstrate that the correction procedures successfully remove both spatial and drift distortions. Specifically, in the absence of intensity noise the distortion removal methods consistently give excellent results with errors on the order of +/- 0.01 pixels. Results from the rigid body motion and tensile loading experiments at 200 x indicate that, after correction for distortions, (a) the displacements have nearly random variability with a standard deviation of 0.02 pixels; (b) the measured strain fields are unbiased and in excellent agreement with previous full-field experimental data obtained with optical illumination; (c) the strain field variability is on the order of 60 microstrain in all components with a spatial resolution on the order of 25 pixels. Taken together, the analytical, computational and experimental studies clearly show that the correction procedures successfully remove both spatial and drift distortions while retaining excellent spatial resolution, confirming that the SEM-based method can be used for both micromaterial and nanomaterial characterization in either the elastic or elastic-plastic deformation regimes.

A combined temporal tracking and stereo-correlation technique for accurate measurement of 3D displacements: application to sheet metal forming

Optical methods that give displacement or strain fields are now emerging significantly in the mechanical sciences. Much work has been done on two-dimensional (2D) displacement/strain measurement from a single camera but the proposed methods give only in-plane strains. A binocular correlation-based stereovision technique has been developed: (a) to measure the three-dimensional (3D) shape of a static object or (b) to measure the strains of an object undergoing some 3D mechanical or thermal stress. In this paper, the application of the stereo-correlation technique to measure accurately the 3D shape of a stamped sheet metal part or the surface strain field undergone by the part during the stamping process is presented.

A speckle texture image generator

We propose a framework for obtaining synthetic speckle-pattern images based on successive transformations of Perlins coherent noise function. In addition we show how a given displacement function can be used to produce deformed images, making this framework suitable for performance analysis of speckle-based displacement/strain measurement techniques, such as Digital Image Correlation, widely used in experimental mechanics.

Camera calibration from multiple views of a 2D object, using a global nonlinear minimization method

An important task in most 3D vision systems is camera calibration. Many camera models, numerical methods and experimental set-ups have been proposed in the literature to solve the calibration problem. We have analysed and tried many methods, and we conclude that the main problems lie in the choice of the numerical methods and on the calibration object. We propose in this paper a method which is based on a camera model that incorporates lens distortion, and involves a nonlinear minimization technique which can be performed using multiple views of a single 2D object and subpixel feature extraction. We present an application for which only a 2D calibration object can be used.

Non-contact Measurement of the Shrinkage and Calculation of Porosity During the Drying of Banana

A novel non-intrusive technique (stereo-correlation) was used to determine the apparent volume of a banana in convective drying condition. The volume was calculated using the 3D Digital Image Correlation method (3D-DIC), which provides the 3D shape of the banana during drying. The combination of this technique and mass measurement allows the calculation of the porosity using the model of Katekawa and Silva[ 1 ] and the graphical interpretation presented by Madiouli et al.[ 2 ] The banana shows an ideal shrinkage at the beginning of drying but stops shrinking at low moisture content, thus increasing the porosity up to 30–35%. The comparison of the experimental shrinkage and the calculated porosity with the experiments deduced from the literature enables us to conclude the effectiveness of the 3D-DIC technique as well as the porosity calculation model.

Evaluation of a charge-coupled-device-based video sensor for aircraft cargo surveillance

We present a new video sensor for multimeasurements in an aircraft cargo compartment called a video sensor unit (VSU). This sensor, based on CCD technology, operates in the near IR (NIR) spectral band to measure temperatures due to overheating and fire events. After a characterization of the measurement chain, a radiometric model is applied to the VSU, enabling the measurement of temperatures ranging from 350 to 900 degreesC with a noise equivalent temperature difference (NETD) lower than +/- 8 degreesC. In the same spectral band (NIR), the VSU can also detect smoke and 3-D load displacements. The geometric model of the VSU is described and the associated calibration procedure is presented.

Automated exterior inspection of an aircraft with a pan-tilt-zoom camera mounted on a mobile robot

Abstract. This paper deals with an automated preflight aircraft inspection using a pan-tilt-zoom camera mounted on a mobile robot moving autonomously around the aircraft. The general topic is image processing framework for detection and exterior inspection of different types of items, such as closed or unlatched door, mechanical defect on the engine, the integrity of the empennage, or damage caused by impacts or cracks. The detection step allows to focus on the regions of interest and point the camera toward the item to be checked. It is based on the detection of regular shapes, such as rounded corner rectangles, circles, and ellipses. The inspection task relies on clues, such as uniformity of isolated image regions, convexity of segmented shapes, and periodicity of the image intensity signal. The approach is applied to the inspection of four items of Airbus A320: oxygen bay handle, air-inlet vent, static ports, and fan blades. The results are promising and demonstrate the feasibility of an automated exterior inspection.

Multi-view dense 3D modelling of untextured objects from a moving projector-cameras system

Structured light methods achieve 3D modelling by observing with a camera system, a known pattern projected on the scene. The main drawback of single projection structured light methods is that moving the projector changes significatively the appearance of the scene at every acquisition time. Classical multi-view stereovision approaches based on the appearance matching are then not useable. The presented work is based on a two-cameras and one single slide projector system embedded in a hand-held device for industrial applications (reverse engineering, dimensional control, etc). We propose a method to achieve multi-view modelling for camera pose and surface reconstruction estimation in a joint process. The proposed method is based on the extension of a stereo-correlation criterion. Acquisitions are linked through a generalized expression of local homographies. The constraints brought by this formulation allow an accurate estimation of the modelling parameters for dense reconstruction of the scene and improve the result when dealing with detailed or sharp objects, compared to pairwise stereovision methods.

Automatic Inspection System for Strip of Preweathered Zinc

UNION MINIERE (UM) is a Belgian firm with an international coverage. It is one of the leading companies in the field of non-ferrous metals. With subsidiaries in several European countries, mainly in Belgium and in France but also in the US, the UM group deals with every step in the production process: mining, smelting, refining, transforming, recycling and engineering.